Opposition spokesman Angel Medina says Maduro's ascension is "a violation of the constitutional order." Critics believe Venezuela's 1999 charter stipulates that the speaker of the National Assembly take power in the event of a presidential death.

Medina also voiced concern that Friday night's swearing-in ceremony is taking place at the same military academy where Chavez is lying in state. He says it set a bad precedent because the military should play no role in politics.